How Submerged Arc Welding Works?

Submerged Arc Welding (SAW) is most commonly used welding process in which the welding arc is travels beneath a blanket of granular flux. In this welding technique a consumable solid or tubular electrode is fed continuously to the weld zone. Simultaneously a blanket of granular fusible flux is poured on the weld zone which submerged the welding arc and protects it from atmospheric contamination. The granulated flux contains silica, lime, calcium fluoride, manganese oxide and other compounds. When the flux is molten, it becomes conductive and provides a current path between the electrode and workpiece. The thick layer of flux covers the molten metal completely and prevents the spatter (cover with drops or spots of metals) and spark as well as cover up the intense ultraviolet radiation fumes produced during the process.

This welding process was discovered in 1935. It is originally developed and patented by Kennedy, Jones and Rothermund.

SAW can be operated in semi-automatic (hand held) or in automatic mode. But normally it is operated in automatic mode.

Power Supply

DC or AC power source can be used for SAW. And for multiple electrode system, combination of DC and AC are commonly used.

The current range utilized in the process is 300 A to 2000 A. for multiple arcs, a current of upto 5000 A have also been used.

Main Parts or Equipment

The main parts or equipment used in submerged arc welding (SAW) process are

Welding head: it is used to feed flux and filler metal to the joint to be weld.

Flux hopper: Here the flux is stored and deliver to the welding joint. It controls the rate of deposition of flux to the welding joint.

Flux: The weld arc is shielded by granular flux. It consists of lime, silica, manganese oxide, calcium fluoride, oxides of calcium and other compounds. It fed into the weld zone by gravity flow through the nozzle of welding head.

When it is molten, it becomes conductive and conducts the current in between the electrode and work. The thick layer of granular flux covers the molten metal completely and prevents the spatter and spark as well as cover up the ultraviolet radiations and fumes which is characteristic of shielded metal arc welding (SMAW) process. The lower part of the flux gets melted and forms slag on the weld pool. It is removed after the welding process gets completed. The upper part of the flux acts as an insulator and promotes deep penetration of heat to the workpiece.

Electrode wire feed Unit: It provides continuous feed of electrode wire to the welding joint. It consists of a reel on which the electrode wire is wounded.

Electrode: Submerged arc welding uses consumable electrode which is a coil of bare round wire of diameter 1.5 mm to 10 mm. It is fed automatically through the welding gun. The composition of electrode depends upon the material being welded. The electrodes are available to weld high carbon steel, mild steel, low and special alloy steels, stainless steel etc. The electrodes are usually coated with copper to prevent rusting and increases electrical conductivity. They are available in straight length and in coils.

Flux recovery unit: It collects the unused flux left after welding. And after recovery it is used again for the welding.

Working of Submerged Arc Welding

In submerged arc welding, first the flux starts to deposit on the joint to be welded. When the flux is cold, is act as an insulator.

The arc is initiated by touching the tool with the workpiece. The arc struck always remains under a thick layer of flux. The heat generated by the arc melts the granular flux.

The flux once melted by heat of the arc, it becomes highly conductive. The current starts to flow in between the electrode and w/p through the molten flux. The flux that is in contact with the atmosphere, which we can see remains granular and can be reused again. The lower melted flux changes to slag and it is a waste which is removed after welding process completes.

At a predetermined speed, the electrode from the reel is continuously fed to the joint to be welded. If welding is semi-automatic, the welding head is moved manually along the joint. In automatic welding setup, a separate drive is used to move either the welding head over the stationary job or job rotates/moves under the stationary welding head.

By using the principle of self-adjusting arc the arc length is kept constant. If the arc length decreases, the voltages of the arc increases and this increase the arc current. Due to this the burn-off rate increases and causing the arc length to increase or lengthen. The reverse phenomena occur in the case the arc length increases more than the normal length.

For controlling penetration and to support large amount of molten metal a backing plate of steel or copper may be use.